Embodiments of the invention relate to an anaesthesia machine arrangement comprising a gas dispenser of an anaesthesia machine connected to a patient circuit comprising a CO2 absorber, a monitor device, a control device and an interface unit, whereby the gas dispenser is configured to deliver a desired concentration of fresh gas to the patient circuit, the desired concentration being set by using the interface unit, the monitor device is configured by using a sample line to monitor gas concentration in the patient circuit and the control device is configured to control the gas dispenser from the basis of the data received from the monitor device to keep the desired fresh gas concentration. The invention relates also to a method in connection with an anaesthesia machine arrangement.
A basic requirement set for devices used in patient care is that they are safe and operationally reliable in the normal use of the device, in fault situations unintentionally caused by a user or in any one-fault situation of the device.
Anaesthesia machines and ventilators used in intensive care and anaesthesia can be mentioned as examples of the devices described above. A patient is normally connected to a device used in patient care, e.g. an anaesthesia machine and ventilator, by means of a patient circuit. From the patient circuit there is a measuring connection to a monitor, which monitors the condition of the patient. Using measuring information on the condition of the patient a healthcare person supervises the condition of a patient and adjusts set values of the device used in patient care so that the measuring information corresponds to the desired value of the moment.
Due to the indirectness and in some circumstances long time constant the exact adjustment of measuring values is slow and difficult, which leads to variation in patient values, and this in turn may have harmful effects on the end result in nursing.
To improve the situation, a variety of solutions have been suggested for automatizing the systems used in the situations described above. In other words it has been suggested that a system, i.e. a machine and not a person, takes automatically care of adjusting steps needed to obtain a result desired. When discussing about automatic systems here we mean that automatic delivery of breathing gases to the patient refers to a system where the desired concentration in breathing gases is set and the machine used keeps it correct by automatically adjusting the fresh gas (FG) flow concentration. When using automatic systems it is however essential that for example in an automatic system delivering a mixture of anaesthetic agent, N2O and oxygen to the patient to be treated, there must be some way to assure that a device failure does not cause the system to deliver wrong concentration to the patient.
In order to achieve a safely level high enough double monitoring is used in the prior art. In double monitoring two or even more monitors are used so that a fault in one monitor can be brought to the user's attention if the monitors show different readings.
The disadvantages of this known technique is the high cost of double monitoring, i.e. double or in some cases even more than double monitoring hardware leads to high costs.
As another example of the prior art a system using one monitor and a sample system can be mentioned. In this system one monitor is used and samples are taken from either the fresh gas used or from some other known gas. The fresh gas concentration is known. If the fresh gas sample readings are wrong one knows that either the anaesthesia machine or monitor does not work correctly. This known system is described in EP Patent 1 140 264 B1.
Prior art systems, i.e. both the traditional person-based systems and the automatic systems have a common disadvantage, which may cause severe risks during anaesthesia. This disadvantage is caused by eventual sampling line leaks. Said leaks can cause the gas sample to be diluted by ambient air. This again can cause the anaesthesia machine used or the person taking care of the steps to be carried out to over deliver, i.e. to overdose the anaesthetic agent to be delivered to the patient treated.
Currently it is difficult to detect a leak. The absence of CO2 or N2O or presence of N2 can in some cases be used for detection but if the leak is small, these known methods are not reliable.